Continuing our series on invasive plants we look at the effects of Giant Hogweed and how it can be controlled. Whilst Giant Hogweed’s effect on the structural integrity of buildings is negligible we have seen reports of mortgage lenders raising concerns over its presence. The dangers to humans, and particularly children, are serious and should it be identified during a pre-purchase or structural survey we would always encourage you to seek further specialist advice.
Heracleum mantegazzianum, commonly known as giant hogweed can grow up to 20ft tall with dinner table sized leaves. Giant Hogweed is an impressive plant that was once planted in gardens and was among many foreign plants introduced to Britain in the 19th century as ornamental plants. It is now widespread throughout the British Isles, especially along riverbanks. By forming dense stands, they can displace native plants and reduce wildlife habitats. It has spread in the north-eastern and north-western United States, and southern Canada. However, it is highly invasive and has spread throughout the whole of Great Britain, primarily favouring river banks but also other areas such as parks, cemeteries and wasteland.
The sap of Giant Hogweed contains toxic chemicals known as furanocoumarins. When these come into contact with the skin, and in the presence of sunlight, they cause a condition called Phyto-photodermatitis: a reddening of the skin, often followed by severe burns and blistering. The burns can last for several months and even once they have died down the skin can remain sensitive to light for many years. Authorities advise that children should be kept away from giant hogweed, that protective clothing, including eye protection, should be worn when handling or digging it, and that if skin is exposed, the affected area should be washed thoroughly with soap and water and the exposed skin protected from the sun for several days
Chemical control spraying can only be carried out during the growing season (March to August), when there is green, leafy material present. In order to be effective, spraying must be carried out before the plant flowers and sets seed, otherwise there will be thousands of additional seeds on the ground ready to grow at some point in the future. Never use a strimmer or chipper on Giant Hogweed material as this can cause sap to become airborne, resulting in injury.
For more information feel free to call The Hopps Partnership.